Glass or glass-ceramic for windows, countertops, and other applications

ABSTRACT

Equipment and manufacturing processes allow for strengthened glass or glass ceramic articles having unique stress profiles, such as high negative tensile stresses and steep tensile stress curves with respect to depth, in strengthened glass or glass ceramic articles that are thin and/or have large-area structures for a given degree of thermal temping.

RELATED APPLICATIONS

This Application claims the benefit of U.S. Application No. 62/031,856 filed Jul. 31, 2014, U.S. Application No. 62/074,838 filed Nov. 4, 2014, and U.S. Application No. 62/147,289 filed Apr. 14, 2015, each of which is incorporated by reference herein in its entirety.

BACKGROUND

Aspects of the present disclosure relate generally to glass or glass-ceramic that has a stress profile for strengthening exterior portions thereof. Glass and glass-ceramic articles, such as sheets of glass, may be used for a broad range of applications. Examples of such applications include use in windows, countertops, containers (e.g., food, chemical), use as a backplane, frontplane, cover glass, etc. for a display device (e.g., tablet, cellular phone, television), use as a high-temperature substrate or support structure, or other applications.

Exterior portions of some types of glass may be strengthened or arranged to have increased strength by exchanging larger for smaller ions near a surface of the glass to impart a negative tensile stress (also called compressive stress) on or near the surface. The negative tensile stress is believed to limit crack initiation and/or propagation. In other cases, exterior portions of some types of glass may be strengthened or arranged to have increased strength by combining two types of glass. For example, by sandwiching molten glass with a higher coefficient of thermal expansion (CTE) between layers of molten glass with a lower CTE, positive tension in the interior glass compresses the outer layers when the glasses cool, again forming negative tensile stress on the surface to balance the positive tensile stress.

Ion exchanging glass can be time-consuming and cumbersome, such as requiring chemical bathing of the glass for extended periods of time. Laminating different types of glasses directly to one another may require complicated manufacturing processes, such as involving a dual-isopipe fusion draw.

A need exists for glass or glass-ceramic articles, made by processes that are less resource intensive and/or cumbersome than conventional processes, such as for use in windows, countertops, devices, etc. with stress profiles of the glass or glass-ceramic articles having strengthened exterior portions thereof to mitigate cracking and damage and with sufficient strength and other properties (e.g., geometry, surface quality, transmittance of visible light, flexibility, etc.) to facilitate the various glass applications.

SUMMARY

Manufacturing processes disclosed herein produce glass and glass-ceramic articles having unique stress profiles for particular structures, geometries and compositions of the glass and glass-ceramic articles.

As discussed in the Background, glass and/or glass ceramic may be strengthened on or near the surface via ion-exchange and use of glass-glass laminates. Glass and/or glass ceramic may also be strengthened on or near the surface via thermal tempering, where the glass or glass ceramic is quickly cooled from outside in, so that the exterior of the glass or glass ceramic is locked at one state and the interior cools and more slowly solidified, resulting in positive tension in the interior of the glass and/or glass ceramic balanced by negative tensile stress exterior thereto. Conventional thermal tempering may be done by contact with heat sink solids or liquids, or via convective cooling with blown air. Ion-exchange is typically used for strengthening of thin glass sheets because the thin articles may be too fragile or too susceptible to warping if thermally tempered by solid or liquid quenching and conventional convective cooling may be too weak to induce sufficient negative tensile stresses. At least some limitations of conventional thermal tempering are overcome by inventive technology of the present application, allowing for strengthened glass or glass ceramic articles that have large negative tensile stresses, such as in bodies without material discontinuities, bodies that are particularly thin and/or flat and/or homogeneous.

Some embodiments relate to a strengthened glass or glass-ceramic article, which includes a first surface, a second surface, and a body extending therebetween. The second surface is on an opposite side of the body from the first surface such that a thickness of the strengthened glass or glass-ceramic article is defined as a distance between the first and second surfaces, a width of the strengthened glass or glass-ceramic article is defined as a first dimension of one of the first or second surfaces orthogonal to the thickness, and a length of the strengthened glass or glass-ceramic article is defined as a second dimension of one of the first or second surfaces orthogonal to both the thickness and the width. The length of the strengthened glass or glass-ceramic article is greater than or equal to the width. At least one of the first or second surfaces has a relatively large surface area, that being at least 2500 mm². The strengthened glass or glass-ceramic article is thin such that the width is greater than five times the thickness. A stress profile of the strengthened glass or glass-ceramic article is such that, at room temperature of 25° C. and standard atmospheric pressure, an interior portion of the strengthened glass or glass-ceramic article is under positive tensile stress and portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion are under negative tensile stress, where the negative tensile stress at least in part fortifies the strengthened glass or glass-ceramic article by limiting initiation and/or propagation of cracks therethrough. A difference in peak values of the positive and negative tensile stresses is at least 200 MPa. Despite the relatively large surface area and/or thin thickness of the strengthened glass or glass-ceramic article, which may limit conventional tempering processes: (a) tensile stress in the stress profile sharply transitions between the positive tensile stress of the interior portion and the negative tensile stress of the portions exterior to and adjoining the interior portion such that a rate of change of the tensile stress is at least 200 MPa divided by a distance of 500 μm and/or (b) the stress profile imparts a high fragmentation potential of the strengthened glass or glass-ceramic article such that when fractured the strengthened glass or glass-ceramic article shatters into particularly small granular chunks, those having an area on either the first or second surface of less than 10 mm². In some such embodiments, the strengthened glass or glass-ceramic article not only shatters, but dices into particularly small granular chunks. Composition of the strengthened glass or glass-ceramic article comprises (a) an amorphous, non-crystalline solid or (b) a polycrystalline solid comprising an amorphous phase and one or more crystalline phases. Further, the composition comprises silicon dioxide. The composition of the strengthened glass or glass-ceramic article located on at least a part of the portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion, under the negative tensile stress, is the same in terms of ion content and chemical constituency as the composition located on at least a part of the interior portion, under the positive tensile stress, such that at least some of the negative tensile stress of the stress profile is independent of a change in the composition of the strengthened glass or glass-ceramic article.

In another embodiment, products are disclosed producible by the processes and apparatuses of the present disclosure, including a glass sheet thinner than 2.5 mm or, desirably, thinner than 2.0 mm and having a thermally-induced stress of the sheet sufficient to produce a number of fragments not less than 40 within an area of 50 by 50 mm of the sheet, in a fragmentation test in which an impact is applied to a predetermined position of the sheet with a hammer or a punch.

In one embodiment, a process or method is provided for strengthening a glass sheet, which includes steps of (1) providing a glass sheet, the glass having a transition temperature, the sheet being above the transition temperature; and (2) cooling the sheet, by conduction more than by convection through a gas to a heat sink sufficiently to fix a thermally-induced surface compression stress, and a thermally-induced central tension stress, of the sheet. Conduction is a process of heat transfer where energy is transmitted through interactions between adjacent molecules, while convection is a process of heat transfer where energy is communicated via motion of a fluid (e.g., air), such as where heated fluid moves away from a heat source and is replaced by cooler fluid. The process of this embodiment may optionally further comprise the further detail of providing a sheet having first and second sheet surfaces, wherein the step of cooling the sheet comprises using a heat sink having a first heat sink surface having apertures therein and facing the first sheet surface across a first gap and a second heat sink surface having apertures therein and facing the second sheet surface across a second gap. The step of cooling the sheet may further comprise feeding the gas to the first and second gaps only through the apertures in the first and second heat sink surfaces, respectively.

According to yet another embodiment, a method is provided for thermally conditioning an article comprising providing an article having a surface and cooling or heating a portion of the surface of the article up to and including the entire surface of the article, the portion having an area, sufficiently to complete a thermal conditioning of the article or of the portion of the surface of the article with the conduction being performed, during at least some time of said heating or cooling, at a rate of at least 450 kW per square meter of the area of the portion. Further, the conduction is performed across a gap between the portion and the heat source or heat sink, the gap having a width g, and an area A_(g), with the gas positioned in the gap and having a heat capacity C_(p) and a thermal conductivity k, taken in the direction of conduction; and the method further includes providing gas to the gap, through apertures in the portion-facing surface of the heat source or the heat sink, at a mass flow rate rim of the gas of less than (2 kA_(g))/(gC_(p)), desirably less than (⅔)(2 kA_(g))/(gC_(p)), desirably less than even ⅘ or 9/10 of (2 kA_(g))/(gC_(p)).

Additional features and advantages are set forth in the Detailed Description that follows, and in part will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings. It is to be understood that both the foregoing general description and the following Detailed Description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying Figures are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments, and together with the Detailed Description serve to explain principles and operations of the various embodiments. As such, the disclosure will become more fully understood from the following Detailed Description, taken in conjunction with the accompanying Figures, in which:

FIG. 1 is digital image from a perspective view of a building with glass windows according to an exemplary embodiment.

FIG. 2 is digital image from a perspective view of a display on a countertop according to an exemplary embodiment.

FIG. 3 is an exploded perspective view of a device including glass or glass ceramic articles according to an exemplary embodiment.

FIGS. 4 and 7 are perspective views of glass or glass ceramic articles according to exemplary embodiments.

FIGS. 5, 6, and 11 are flowchart diagrams of processes according to exemplary embodiments.

FIG. 8 is a conceptual diagram from a side perspective of manufacturing equipment according to an exemplary embodiment.

FIG. 9 is a conceptual diagram from a side perspective of manufacturing equipment according to another exemplary embodiment.

FIG. 10 is a conceptual diagram from a perspective view of the manufacturing equipment of FIG. 9.

FIG. 12 is a graphical representation of estimated tensile stress versus thickness for a glass or glass ceramic article according to an exemplary embodiment.

FIG. 13 is a digital image of a fractured glass or glass ceramic article according to an exemplary embodiment.

FIG. 14 is a plot of fragmentation per square centimeter as a function of positive tensile stress from experiment.

FIG. 15 is a plot of the magnitude of negative tensile stress at the surface as a function of initial hot zone temperature from experiment, showing a threshold to achieve dicing.

DETAILED DESCRIPTION

Before turning to the following Detailed Description and Figures, which illustrate exemplary embodiments in detail, it should be understood that the present inventive technology is not limited to the details or methodology set forth in the Detailed Description or illustrated in the Figures. For example, as will be understood by those of ordinary skill in the art, features and attributes associated with embodiments shown in one of the Figures or described in the text relating to one of the embodiments may be applied to other embodiments shown in another of the Figures or described elsewhere in the text.

Referring to FIG. 1, a structure 1010, such as building, house, vehicle, etc., includes a glass or glass ceramic article 1012 in the form of a window, a portion of walls (e.g., surfaces), dividers, etc. In contemplated embodiments, the glass or ceramic article 1012 may be strengthened such that the glass or ceramic article 1012 has a negative tensile stress on or near surfaces thereof, balanced by a positive tensile stress internal thereto, as disclosed herein. Further, the glass or glass ceramic article 1012 may have a composition that resist chemicals and/or corrosion as may be present in outdoor environments by having a relatively high silicon dioxide content, such as at least 70% silicon dioxide by weight, such as at least 75% by weight.

According to an exemplary embodiment, the glass or glass ceramic article 1012 has major surfaces orthogonal to a thickness thereof (see generally sheet 2110 as shown in FIG. 7), where the major surfaces have a large area (e.g., at least 5 cm², at least 9 cm², at least 15 cm², at least 50 cm², at least 250 cm²) relative to glass or glass ceramic articles used in other applications (e.g., lenses, battery components, etc.). In contemplated embodiments, total transmission through the glass or glass ceramic articles 1012 is at least about 50% (e.g., at least 65%, at least 75%) from wavelengths of about 300 nm to about 800 nm, when the glass or glass ceramic article 1012 has thicknesses as disclosed herein, such as a thickness of less than 5 cm, less than 3 cm, less than 2 cm, less than 1.75 cm, less than 1.5 cm, less than 1 cm, less than 5 mm, less than 3 nun, less than 2 mm, less than 1.75 mm, less than 1.5 mm, less than 1 mm, less than 0.8 mm, less than 0.6 mm, less than 0.5 mm, less than 0.4 mm, less than 0.2 mm, and/or at least 10 micrometers, such as at least 50 micrometers.

In some embodiments, the thermally strengthened glass sheets have high thinness i.e., are particularly thin. Because very high heat transfer rates can be applied, significant thermal effects, for example CTs of at least 10 or even at least 20 MPa, can be produced in sheets of SLG of less than 0.3 mm thickness. In fact, very thin sheets, sheets at least as thin as 0.1 mm, can be treated. Specific levels of thermal stresses achieved and achievable, considered as a function of thickness and other variables, are described in further detail below.

Thin thicknesses of the glass or glass ceramic article 1012 may not harm the function of the glass or glass ceramic article 1012 in architectural, automotive, or other applications relative to conventional articles because the strength of the glass or glass ceramic article 1012 may be correspondingly improved by inventive processes disclosed herein. Thin glass or glass ceramic articles 1012 may be particularly useful in such architectural, automotive, or other applications because the glass or glass ceramic article 1012 may be lighter than conventional such articles, reducing weight of the corresponding overall structure. For automobiles, a result may be greater fuel efficiency. For buildings, a result may be sturdier or less resource-intensive structures. In other contemplated embodiments, glass or glass ceramic articles disclosed herein may have areas of lesser magnitude, greater thicknesses, transmit less light, and/or may be used in different applications, such as those disclosed with regard to FIGS. 2-4, for example.

Referring to FIG. 2, a surface 1110 includes a glass or glass ceramic article 1112, manufactured as disclosed herein and/or with a stress profile and structure as disclosed herein, that functions as a countertop and/or as a portion of a display. In some embodiments, total transmission through the glass or glass ceramic articles 1012 is at least about 30% (e.g., at least 50%) from infrared wavelengths of about 800 nm to about 1500 nm, facilitating use of the surface 1110 as a cooktop. In some embodiments, the glass or glass ceramic article 1112 has a coefficient of thermal expansion (CTE) from about 10×10⁻⁷° C.⁻¹ to about 140×10⁻⁷° C.⁻¹, about 20×10⁻⁷° C.⁻¹ to about 120×10⁻⁷° C.⁻¹, about 30×10⁻⁷° C.⁻¹ to about 100×10⁻⁷° C.⁻¹, about 40×10⁻⁷° C.⁻¹ to about 100×10⁻⁷° C.⁻¹, about 50×10⁻⁷° C.⁻¹ to about 100×10⁻⁷° C.⁻¹, or about 60×10⁻⁷° C.⁻¹ to about 120×10⁻⁷° C.⁻¹. In particular, the processes are ideally suited for glass compositions having moderate to high CTEs. Example glasses that work well with the processes described herein include alkali aluminosilicates, such as Corning's® Gorilla® Glasses, boroaluminosilicates, and soda lime glasses. In some embodiments, the glasses used have CTEs of greater than 40, greater than 50, greater than 60, greater than 70, greater than 80, or greater than 90×10⁻⁷/° C. Some such CTEs may be particularly low for thermal tempering as disclosed herein, where the degree of negative tensile stress is no more than 50 MPa and/or at least 10 MPa.

Referring to FIG. 3, a device 1210 (e.g., handheld computer, tablet, portable computer, cellular phone, television, display board, etc.) includes one or more glass or glass ceramic articles 1212, 1214, 1216, manufactured as disclosed herein and/or with a stress profile and structure as disclosed herein, and further includes electronic components 1218 and a housing 1220. In contemplated embodiments, the housing 1220 may be or include a glass or glass ceramic article as disclosed herein. In contemplated embodiments, a substrate 1222 for the electronic components 1218 may be a glass or glass ceramic article as disclosed herein.

According to an exemplary embodiment, glass or glass ceramic articles 1212, 1214 of the device 1210 are boro-aluminosilicate glasses. In some embodiments, glass or glass ceramic articles 1212, 1214 are generally non-alkali glasses, yet still have stress profiles and structures as disclosed herein. Such composition may reduce the degree of relaxation of the glass, facilitating coupling of transistors thereto.

In some embodiments, the glass or glass ceramic articles 1212, 1214 may function as frontplane and backplane substrates and the glass or glass ceramic article 1216 may function as a cover glass in the device 1210. According to an exemplary embodiment, the glass or glass ceramic article 1216 of the device 1210 is an alkali-aluminosilicate glass. Such composition may allow the glass or glass ceramic article 1216 to be strengthened by thermal tempering, as disclosed herein, and additionally be strengthened by ion-exchange, providing a particularly high degree of negative tensile stress (e.g., at least 200 MPa, at least 250 MPa) at or near surfaces thereof. In other embodiments, the glass or glass ceramic article 1216 may include sodium carbonate, calcium oxide, calcium magnesium carbonate, silicon dioxide (e.g., at least 70% by weight), aluminum oxide, and/or other constituents; and may strengthened by the inventive processes disclosed herein. The glass or glass ceramic article 1216 may be particularly thin or otherwise structured, such as having any of the dimensions as disclosed herein.

Referring now to FIG. 4, a glass or glass ceramic article 1310, manufactured according to processes disclosed herein and with structural properties and a stress profile as disclosed herein, has curvature and/or a variable cross-sectional dimension D. Such articles may have thicknesses disclosed herein as an average of dimension D or as a maximum value of dimension D. While the glass or glass ceramic article 1310 is shown as a curved sheet, other shapes, such as more complex shapes, may be strengthened by processes disclosed herein. In contemplated embodiments, the glass or glass ceramic article 1310 may be used as a window for an automobile (e.g., sunroof), as a lens, as a container, or for other applications.

Strengthening processes and equipment disclosed herein (see generally FIGS. 5-6 and 8-11) allow for strengthening of glass or glass ceramic articles (see generally FIGS. 1-4, 7, and 12-13) by an inventive form of thermal tempering. The processes allow for steep tensile stress versus thickness/depth curves (see generally FIG. 12), particularly steep in slope near the surface of the glass or glass ceramic articles, which enable strengthening of the glass or glass ceramic articles to particularly high levels of negative tensile stress for a given thickness near the surface of the respective articles, without requiring strengthening by ion-exchange or laminating different glasses. However, the thermal tempering processes disclosed herein may be augmented with ion-exchange or applied to glass-to-glass laminations. The thermal tempering processes disclosed herein enable particularly high levels of strengthening in large-area articles (e.g., sheets) that may be too large for strengthening via conventional thermal tempering methods, such as due to alignment limitations of contact quench equipment, cooling rate limitations of conventional convention, and/or warping damage associated with liquid quench tempering. The processes disclosed herein uniquely allow high levels of strengthening in particularly thin sheets that may be too thin for strengthening via conventional tempering methods, such as due sensitivity to breakage or fracture of the thin glass or glass ceramic articles during the strengthening process and associated contact forces with solid or liquid quenching and/or due to the cooling rate limitations of conventional convention tempering. However, in other contemplated embodiments, glass or glass ceramic articles as disclosed herein may be manufactured with at least some solid or liquid quenching, such as in combination with the unique strengthening processes disclosed herein.

While the methods, equipment, and articles disclosed herein may be described in terms of operation on glass or of being glass, in alternate embodiments, the material is a glass ceramic. One embodiment of a method according to the present disclosure is illustrated in the flow chart of FIG. 5. The method or process 100 comprises the step 110 of providing a sheet comprising a glass, the glass having a transition temperature, with the sheet being above the transition temperature; and the step 160 of cooling the sheet, by conduction more than by convection through a gas to a heat sink sufficiently to complete the strengthening process, that is, sufficiently to fix a thermally-induced surface compression stress, and a thermally-induced central tension stress, of the sheet.

Referring to FIG. 5, a method 100 includes a step 110 of providing a glass sheet that is at a temperature above a transition temperature of the glass sheet. The method 100 further includes a step 160 of cooling the sheet, where the cooling is (1) by conduction more than convention processes, through a gas to a heat sink; and (2) enough to complete the strengthening process. The step 110 may precede the step 160.

Referring to FIG. 6, a flowchart of the method 100 includes the step 110, providing a glass sheet (see generally sheet 2110 as shown in FIG. 7) with first and second surfaces at a temperature above a transition temperature of the glass of the sheet. As part of, or as preparation for, the cooling step 160, the method 100 further comprises, in step 120, providing a heat sink (whether as a single piece or in separate pieces) having first and second heat sink surfaces (see generally FIGS. 8-10), each having apertures therein; and, in steps 130A and 130B, positioning the first heat sink surface facing the first sheet surface across a first gap and positioning the second heat sink surface facing the second sheet surface across a second gap. The method 100 further comprises in step 160 cooling the sheet, by conduction more than by convection through a gas to the heat sink, sufficiently to complete the strengthening process, that is, sufficiently to fix a thermally-induced surface compression stress, and a thermally-induced central tension stress, of the sheet. The step 160 of cooling the sheet also includes feeding the gas to the first and second gaps through the apertures only.

These and some other related methods of the present disclosure discussed herein use conduction as the dominant mode of cooling, but the conduction is mediated through a gas. Instead of a solid-to-gas (glass to air) heat exchange, this embodiment of a process and method according to the present disclosure may be viewed as effectively a solid-to-solid (glass to heat sink) heat exchange, mediated across a small gap by a small amount of gas, both to begin and to complete the cooling that produces thermal strengthening.

Applicants believe that dominance of conductive heat transfer may increase the rate of heat transfer relative to dominance of convection. Further the use of conduction, through a gas, may mitigate contact damage, warping, shaping, etc. associated with conventional liquid or solid quench tempering. Use of a gas as an intermediate conductor preserves the surface quality of the processed articles by avoiding solid-to-solid contact. Mediating the high conduction rates through a gas also avoids liquid contact. Some types of liquid quenching can introduce unwanted distortions, spatial variation in tempering and contamination of the glass surfaces. These embodiments essentially provide non-contact (except by a gas) but very high-rate cooling. In other embodiments, as discussed above, solid- or liquid-contact may be included.

Applicants believe that because conduction, ultimately solid-to-solid, carries more of the heat flow than convection, the cooling rate may not be dependent or as dependent on air velocity and volume, when compared to convection-based tempering. With the process 100 of FIG. 6, gas flow and gap size may instead be adjusted for stiffness of the gas in a gap for flattening and/or otherwise shaping a sheet, or for maintaining sheet flatness and/or shape during thermal strengthening, as well balancing ease of sheet handling and high cooling rates, for example.

The process 100 of FIG. 6 may also mitigate risks of deformation of hot thin sheets by the high speed, high volume air flows of convection-based tempering, and is expected to allow softer, higher temperature glass to be handled without distortion, further improving the achievable degree of tempering. Accordingly, glass or glass ceramic articles as disclosed herein may be particularly flat, consistent in thickness, smoothness etc., as further discussed below. The process 100 of FIG. 6 also may keep high-flow cooler air from entering and cooling nearer parts of a respective furnace used to heat the sheet.

According to other embodiments or additional aspects of the present disclosure, the manufacturing equipment 290 (FIG. 8) uses very small apertures 292 (FIG. 8) or pores (e.g., through-pores in a porous substrate) in the heat sink face 202 a, 202 b to provide the gas within the gap 240. In some embodiments, such very small apertures 292 or pores function as individual flow restrictors, providing high performance gas-bearing dynamics such as high levels of stiffness and homogeneity of support to the sheet, as well as high homogeneity of thermal strengthening effects to avoid or limit stress birefringence. Further, because very small pores or apertures 292 may be and are used, the relative amount of solid matter at the surface of the heat sink facing the sheet surface across the gap is maximized, thereby maximizing the effective solid-gas-solid heat flow.

According to another embodiment, use of such apertures 292 as the only path for providing gas to the gap 240, and desirably using apertures 292 that lie in directions close to normal to the heat sink surface 202 a, 202 b, ensures that air-bearing type dynamics are optimized, and not compromised by gas flows from larger apertures, or from sources other than through the heat sink surface(s) 202 a, 202 b adjacent to the sheet 200, or by other excessive lateral flow. In other embodiments gas may be provided to the gap 240 via other sources, such as in addition to the apertures 292 or pores. Accordingly, aspects of the present disclosure allow for power and energy savings by use of the low gas flows and solid-gas-solid conduction, such as relative to conventional convective tempering processes.

Conservatively estimated peak power levels for operation of processes disclosed herein, when active cooling of the heat sink surfaces 202 a, 202 b is added in, assuming the thermal load equivalent of a 300° K drop in glass sheet 200 temperature, is all handled within an active cooling system having a thermal-to-mechanical (or electrical) efficiency ratio of 7.5 to 1, all within a time limit of 2.1 seconds for processes corresponding approximately to glass sheets 200 actually tempered in an experimental apparatus as described herein below.

Yet another advantage resulting from cooling by conduction and of setting air flow (or gas flow) rates as low as possible is that the use of gases other than air is economically very feasible. In some embodiments, the gas is helium. Even helium with prices assumed at multiples of those available today becomes an economically viable alternative at low flow rates, and offers thermal conductivity about five times that of air.

The following is Applicants' understanding of underlying theory. It may well occur to one of ordinary skill in the art of glass tempering, in which conduction effects are normally so small as to be commonly ignored in favor of analysis of convection and radiation alone, to ask whether sufficiently high cooling rates for thin glass sheets (such as at 2 millimeters and below) are actually achievable by conduction through a gas such as air—and if so, whether such rates are achievable at practical gap sizes. As a first point, it must be noted that although the nominal thermal conductivity of (dry) room temperature air (25° C.) is 0.026 W/m·K, in the context of thermal tempering by conduction as in the present disclosure, the thermal conductivity of the gas must be evaluated in the direction of conduction, which is along a thermal slope. Air at high temperature, at or near the surface of the sheet to be or being cooled, has significantly higher thermal conductivity than air at a lower temperature such as air at or near room temperature, at or near the surface of the heat sink. Using the approximation of assuming air over the whole gap to be at the average temperature of the two facing surfaces, at the start of tempering, a glass sheet may be at a temperature of 670° C. for example, while the heat sink surface may start at 30° C., for example. Accordingly, the average temperature of the air in the gap would be 350° C., at which dry air has a thermal conductivity of about 0.047 W/m·K, more than 75% higher than its thermal conductivity at room temperature, and sufficiently high to conduct large amounts of heat energy through gaps of practical size as discussed below, assuming the sheet is finished to a reasonably high degree of surface and thickness consistency.

To illustrate, the conductive component of the rate of heat transfer through a gap of distance g which gap has an area A_(g) (in a direction everywhere perpendicular to the gap distance g) may be given by:

$\begin{matrix} {Q_{cond} = \frac{A_{g}{k\left( {T_{S} - T_{HS}} \right)}}{g}} & (1) \end{matrix}$

where k is the thermal conductivity of the material (gas) in the gap evaluated in the direction of (or opposite of) heat conduction, T_(S) is the temperature of the glass surface and T_(HS) is the temperature of the heat sink surface (or the heat source surface, for other embodiments). As mentioned above, to evaluate k rigorously would require integrating the thermal conductivity of the gas along (or against) the direction of conductive heat flow, as the thermal conductivity of the gas varies with temperature—but a good approximation of k may be taken as the value of k for the gas in the gap when at the average of the temperatures of the two surfaces, T_(S) and T_(HS).

Reframing equation (1) in units of heat transfer coefficient, in units of heat flow power per meter squared per degree Kelvin gives:

$\begin{matrix} {\frac{Q_{cond}}{A_{g}\left( {T_{S} - T_{HS}} \right)} = \frac{k}{g}} & (2) \end{matrix}$

so the effective heat transfer coefficient for conduction across the gap is merely the thermal conductivity of the medium in the gap (air in this test case) (in units of W/mK) by the length of the gap (in meters), giving a value of Watts per meter squared per degree of temperature difference.

Table I shows heat transfer coefficients (k/g), due to conduction alone, for air and helium filled gaps, from 10 micrometers up to 200 micrometers in steps of 10 micrometers each. An air gap of a little less than 40 micrometers should be small enough to allow full tempering of 2 millimeter thick glass by conduction effects alone, while with use of Helium (or Hydrogen, with similar thermal conductivity but requiring careful handing) a gap of about 200 micrometers should be small enough. And this analysis is for conduction only, neglecting radiation and convection, which will not be zero. While slightly less than 40 micrometers is a rather small gap, planar porous air bearings in conveyor applications may generally be run with gaps of as low as 20 micrometers reliably. Thus 37 micrometers is within the realm of the reasonably achievable for an air gap fed by pores in the heat sink surface. Using helium or hydrogen simply relaxes the gap size by about 5 times for the same heat transfer coefficient, (or increases the heat transfer coefficient available for quenching by about 5 times at the same gap size). So even with air the spacing is not impractical, and with high conductivity gases, the gap spacing is relatively easy to achieve, even for sheet thicknesses smaller than 2 millimeters.

TABLE I Air Helium conductivity (W/m/K) 0.047 conductivity (W/m/K) 0.253 heat trans coeff. heat trans coeff. Gap (m) W/m²/K cal/s/cm² Gap (m) W/m²/K cal/s/cm² 0.00001 4700 0.11226 0.00001 25300 0.604291 0.00002 2350 0.05613 0.00002 12650 0.302145 0.00003 1566.67 0.03742 0.00003 8433.33 0.20143 0.00004 1175 0.028065 0.00004 6325 0.151073 0.00005 940 0.022452 0.00005 5060 0.120858 0.00006 783.333 0.01871 0.00006 4216.67 0.100715 0.00007 671.429 0.016037 0.00007 3614.29 0.086327 0.00008 587.5 0.014032 0.00008 3162.5 0.075536 0.00009 522.222 0.012473 0.00009 2811.11 0.067143 0.0001 470 0.011226 0.0001 2530 0.060429 0.00011 427.273 0.010205 0.00011 2300 0.054936 0.00012 391.667 0.009355 0.00012 2108.33 0.050358 0.00013 361.538 0.008635 0.00013 1946.15 0.046484 0.00014 335.714 0.008019 0.00014 1807.14 0.043164 0.00015 313.333 0.007484 0.00015 1686.67 0.040286 0.00016 293.75 0.007016 0.00016 1581.25 0.037768 0.00017 276.471 0.006604 0.00017 1488.24 0.035547 0.00018 261.111 0.006237 0.00018 1405.56 0.033572 0.00019 247.368 0.005908 0.00019 1331.58 0.031805 0.0002 235 0.005613 0.0002 1265 0.030215

In addition to cooling through a gas by conduction more than by convection, another embodiment of the present disclosure includes heating (or heating and/or cooling) through a gas by conduction more than by convection. Regarding the relative contributions of conduction and convection, whether for heating or cooling, the convective Q_(conv) component of the rate heat transfer across the gap (or gaps) may be given by:

$\begin{matrix} {Q_{conv} = {e\overset{.}{m}{C_{p}\left( {\frac{T_{S} + T_{HS}}{2} - T_{i}} \right)}}} & (3) \end{matrix}$

where in is the mass flow rate of the gas, Cp is the specific heat capacity of the gas, T_(i) is the inlet temperature of the gas as it flows into the gap, and e is the effectiveness of the heat exchange between the gas flowing in the gap and the sheet surface and the surface of the heat sink/source (the “walls” of the gap). The value of e varies from 0 (representing zero surface-to-gas heat exchange) to 1 (representing the gas fully reaching the temperature of the surfaces). The particular value of e can be computed by those skilled in the art of heat transfer using, for example, the number of transfer units e-NTU method.

Typically however, if the gap 240 between the surface 200 a, 200 b of the sheet 200 and the surface 202 a, 202 b of the heat sink/source is small, the value of e will be very nearly equal to 1, meaning the gas heats up nearly completely—to equal, on average, the average of the temperature of the two surfaces on either side—before it leaves the gap 240. We will assume e=1, thus overestimating the rate of heat transfer due to convection, but only slightly. With the gas being supplied to the gap 240 through the surface 202 a, 202 b of the heat sink/source, we can further assume the initial temperature of the gas in the gap 240 is the same as the temperature of the surface 202 a, 202 b of the heat sink/source (T_(i)=T_(HS)). The rate of heat transfer due to convection may then be simplified to:

$\begin{matrix} {Q_{conv} = {\overset{.}{m}{C_{p}\left( \frac{T_{S} - T_{HS}}{2} \right)}}} & (4) \end{matrix}$

At the temperatures typically useful for heat strengthening or heat treating of glass and similar materials, radiative heat transfer out of the sheet under treatment is relatively small. To cool (or heat, assuming the amount of radiation from the heat source when heating is not too high) the sheet 200 principally by conduction, in the area of the gap 240, thus requires only that:

Q_(cond)>Q_(conv)  (5)

Combining (5) with equations (1) and (4) gives the following conditional:

$\begin{matrix} {\frac{k}{g} > \frac{\overset{.}{m}C_{p}}{2A_{g}}} & (6) \end{matrix}$

which, when held, will essentially ensure that the sheet 200, in the area of the gap 240 at issue, will be cooled (or heated) principally by conduction. Accordingly, the mass flow rate in of the gas should be less than 2 kA_(g)/gC_(p), or 2 k/gC_(p) per square meter of gap area, desirably even lower in most cases. In particular, it is desirable that {dot over (m)}<B·(2 kA_(g)/gC_(p)), where B is a positive constant less than one, desirably having a value of ⅔ or less, or even ⅘ or 9/10 or less. Generally, {dot over (m)} should be kept as low as possible, consistent with the needs of using the gas flow to control the position of the sheet 200 relative to the heat sink surface(s) 202 a, 202 b or the position of the heat exchange surfaces themselves.

A diagrammatic cross-section of a glass sheet being cooled by conduction more than by convection is shown in FIG. 8. A hot glass sheet 200 has two major surfaces 200 a, 200 b each facing a respective surface 202 a, 202 b of a two-piece heat sink 202 across respective gaps 204 a and 204 b. Air (or other gas) is fed through the surfaces 202 a, 202 b as represented by the arrows 230, to supply the gaps 204 a, 204 b, and to assist in keeping the glass sheet centered within the heat sink 202. Air (or other gas) leaves through the edges of the heat sink 202 as shown by arrows 240. By choosing the size of the gaps 204 a, 204 b and the gas and the flow rate of the gas 230 in accordance with the preceding paragraph and the other discussion above, the glass sheet 200 will be cooled more by conduction than convection.

FIG. 9 is a schematic cross-sectional diagram of an experimental apparatus 410 according to the present disclosure, in which a glass article 412 (hot glass), 414 (cold glass) can be cooled through a gas into a heat sink 418 more by conduction than by convection. The apparatus 410 of FIG. 9 includes a hot zone 420, a cold zone 422, and a transition gas bearing 424 in between, by which a glass article 412 (hot glass), 414 (cold glass) may be shuttled from a hot zone 420 to a cold zone 422 such that no contact occurs between the glass 412 (hot glass), 414 (cold glass) and the bearings 424, 426, 428.

According to an exemplary embodiment, the hot zone 420 has gas bearings 426 with cartridge heaters 428 inserted into holes through the bearings 428, which serve to heat the hot zone gas 420 bearings 426 up to a desired starting process temperature. The glass 412 (hot glass), 414 (cold glass) is floated within the hot zone 420 gas bearings 426 for a duration long enough to bring the glass 412 (hot glass), 414 (cold glass) fully up to the temperature of the hot zone 420. The bearing gaps (see, e.g., gaps 204 a, 204 b of FIG. 8) between the hot zone 420 gas bearings 426 and the glass 412 may be very large, on the order of 0.05″ (1.27 mm) to 0.125″ (3.175 mm), since the glass 412 may be heated up relatively slowly and thermal radiation from the hot gas bearings 426 into the glass 412 is adequate for this purpose.

Once the glass article 412 is up to its desired starting process temperature (typically equal to the temperature of the hot gas bearings 426 within some small amount), then the glass article 412 can be shuttled rapidly from the hot zone 420 to the cold zone 422. This can be done by (1) tilting the entire assembly 410 such that gravity acting on the glass article 412 forces it to shuttle to the cold zone 422, (2) blocking off the gas flow from the entrance 430 of the hot zone 420 (the sides are enclosed), thereby forcing all of the air 416 emanating from all of the air bearings 426 to exit from the exit 432 of the cold zone 422, causing fluid forces to be exerted on the glass article 412 (hot glass), 414 (cold glass) and causing the glass article 412 (hot glass), 414 (cold glass) to shuttle rapidly to the cold zone 422, or (3) a combination of (1) and (2). Note that the solid material 440 (FIG. 10) thickness under the surface of the transition gas bearing 424 is very thin; this is done to reduce heat conduction from the hot zone 420 to the cold zone 422.

According to an exemplary embodiment, the transition gas bearing 424 serves as a thermal break between the two zones 420, 422 and the transition gas bearing 424 serves to transition from the large gaps between the bearing 426 and the sheet 412 of the hot zone 420 down to the small gaps of the cold zone 422. Once the glass 412 is shuttled into the cold zone 422, shown as glass 414, it may be stopped from exiting the exit 432 by a stop gate 434. Once the glass 414 has cooled sufficiently that the center has passed the glass transition (in the case, for example, of 1 mm thick soda lime glass to somewhere below about 490° C., corresponding in this example to about 325° C. at the surface), the stop gate 434 can be removed and the glass 414 can be removed from the assembly 410, fully tempered. If desired, the sheet 414 may be left in the cold zone 422 until somewhere near room temperature before removal.

According to an exemplary embodiment, the gas bearing 428 surfaces facing the sheet 414 of the “cold” gas bearing 428 (FIG. 9) serve as the two heat sink 418 surfaces and the gas cushion in the cold gas bearing 428 serves as the gas through which the glass sheet 414 is cooled by conduction more than by convection. Desirably, the material heat sink 418 (cold bearing) surfaces, stainless steel in the experimental model, may be relatively thick compared to the transition bearing 424 surfaces, as shown in FIG. 9, such that heat sink 418 can easily accept relatively large amounts of thermal energy.

FIG. 10 is a cut-away perspective cross section of the apparatus 410 of FIG. 9, showing additionally a load/unload zone 436 next to the cold end of the apparatus 410. In some embodiments, plenums 438 in the apparatus 410 receive air/gas that is then directed to the apertures/pores (see also apertures 292, as shown in FIG. 8).

Table II below shows results obtained by the methods of the present disclosure (indicated as “Source of Method” I in the table), and a figure of merit, Alpha, that is a rough measure of the coefficient of heat exchange obtained within the tempering process. Alpha is given by:

$\begin{matrix} {{Alpha} = \frac{CS}{\left( {t \cdot {CTE} \cdot E} \right)}} & (7) \end{matrix}$

where CS is physical compressive stress (in MPa), t is thickness in millimeters, CTE is the coefficient of thermal expansion in ° C.⁻¹, and E is the elasticity of the glass in (MPa), and yields units in ° C./mm.

TABLE II Sample Source of Thickness Alpha No. Method Glass (mm) CS (MPa) CTE (1/C) E (MPa)** (C/mm) 1 I SLG 1.84 150 9.20E−06 68900 129 2 I SLG 1.84 172 9.20E−06 68900 147 3 I SLG 1.07 190 9.20E−06 68900 280 Samples 1 and 3 are repeatable values obtained from the disclosed processes, sample 1 using air and sample 3 using helium as the gas in the process. Sample 2 represents a “champion” value using air within the present process, that is, not reliably repeatable to date. Glass samples processed by the processes of the present disclosure (samples 1-3) all exceeded an Alpha at 117° C./mm. Applicants believe that the slope of Alpha with thickness may have an inherent trend lower with lower glass thickness. Glass disclosed herein has an Alpha of greater than 20t+77, where t is in mm in some embodiments.

Additional embodiments of the processes of the current disclosure including heating through a gas by conduction more than convection. Such a process or method 300 is illustrated in the flow chart of FIG. 11. The method 300 there shown includes two main steps 310, 320. The first step, step 310 involves simply providing an article having a surface. The second step, step 320 involves heating or cooling a portion of the surface of the article up to and including the entire surface of the article. The portion of the surface has an area with the following properties of the step 320: (1) cool/heat is performed by conduction more than by convection through a gas from or to a heat source or a heat sink or source (step 320 sub-part 320 a in FIG. 11), (2) is performed sufficiently to complete thermal conditioning of the article or the portion of the surface of the article (step 320 sub-part 320 b in FIG. 11), and (3) the conduction of the cooling/heating of step 320 is performed at a high rate of heat transfer, such as at least 450 kW/m² of the area of the portion (step 320 sub-part 320 c in FIG. 11).

One characteristic of certain embodiments of the present disclosure is that high rates of thermal power transfer are possible—even thermal power transfer rates as high as 550, 650, 750, 1000, and 1200 kW or more per square meter are possible through conduction alone, using air. Using helium (or hydrogen) makes even significantly higher rates reasonably achievable. Such rates may be useful for thermal processing of all kinds, including heating and cooling during tempering, edge strengthening of glass, firing or sintering of ceramics, glasses, or other materials, and so forth.

In yet another aspect of the present disclosure, tight control is provided over the thermal history and the heat distribution in the treated article, since the heat is extracted or delivered primarily by conduction, yet surface smoothness and quality are preserved. Accordingly, it will be possible to use the apparatuses and methods of the present disclosure to intentionally vary the stress profile from the strengthening process, both in the thickness direction and in the directions in which the plane of the sheet lies, by varying gaps, varying heat sink/source materials, varying heat sink/source temperatures, varying the gas mixture—and all these may be varied by position along the path of the sheet as it moves, or across the path of the sheet, or potentially in time also, not merely with position (for most of the variables).

Also, because the cooling (or heating) is largely conductive in many embodiments, issues not present in convection-dominated cooling are addressed here. Namely, for tempering of a large thin sheet, the sheet is desirably either (1) introduced very quickly, into the cold zone, at higher speeds than those typically used in convection-based quenching, or, (2) the process is operated in a quasi-continuous mode, in which multiple sheets are tempered one after the other in a continuous stream with little space between them, and in which the heat sink is actively cooled such that it reaches a thermal equilibrium so that the front and trailing edges of the large sheets have the same thermal history.

Glass according to the present disclosure is useful to form at least one sheet of a glass-polymer-interlayer-glass laminate, such as used in many automotive glass sidelights. Stronger and thinner laminates can be produced, resulting in weight and cost savings and fuel efficiency increases. Desirably, a thermally strengthened thin sheet may be cold bent (see generally FIG. 4) and laminated to a formed thicker glass, providing an easy and reliable manufacturing process not requiring any hot forming of the thin sheet.

Referring now to FIG. 7, a strengthened glass or glass-ceramic article 2110 (e.g., sheet, beam, plate), includes a first surface 2112, a second surface 2114 (dotted line to back side of the article 2110, which may be translucent as disclosed herein), and a body 2116 extending therebetween. The second surface 2114 is on an opposite side of the body 2116 from the first surface 2112 such that a thickness T of the strengthened glass or glass-ceramic article 2110 is defined as a distance between the first and second surfaces 2112, 2114, where the thickness T is also a dimension of depth. A width W of the strengthened glass or glass-ceramic article 2110 is defined as a first dimension of one of the first or second surfaces 2112, 2114 orthogonal to the thickness T. A length L of the strengthened glass or glass-ceramic article 2110 is defined as a second dimension of one of the first or second surfaces 2112, 2114 orthogonal to both the thickness T and the width W.

According to an exemplary embodiment, the length L of the strengthened glass or glass-ceramic article 2110 is greater than or equal to the width W, such as greater than twice the width W, greater than five times the width W, and/or no more than fifty times the width W. In some such embodiments, the width W of the strengthened glass or glass-ceramic article 2110 is greater than or equal to the thickness T, such as greater than twice the thickness T, greater than five times the thickness T, and/or no more than fifty times the thickness T.

In some embodiments, such as for applications disclosed with regard to FIGS. 1-4, for example, the length L of the glass or glass-ceramic article 2110 is at least 1 cm, such as at least 3 cm, at least 5 cm, at least 7.5 cm, at least 20 cm, at least 50 cm, and/or no more than 50 m, such as no more than 10 m, no more than 7.5 m, no more than 5 m. In some such embodiments, the width W of the glass or glass-ceramic article 2110 is at least 1 cm, such as at least 3 cm, at least 5 cm, at least 7.5 cm, at least 20 cm, at least 50 cm, and/or no more than 50 m, such as no more than 10 m, no more than 7.5 m, no more than 5 m. Referring to FIG. 7, glass or glass ceramic is the form a sheet 2110 and has a thickness T that is thinner than 5 cm, such as 2.5 cm or less, 1 cm or less, 5 mm or less, 2.5 mm or less, 2 mm or less, 1.7 mm or less, 1.5 mm or less, 1.2 mm or less, or even 1 nun or less in contemplated embodiments, such as 0.8 mm or less; and/or the thickness T is at least 10 μm, such as at least 50 μm, at least 100 μm, at least 300 μm.

In other contemplated embodiments, the glass or glass ceramic article may be otherwise sized as disclosed herein, or otherwise. In contemplated embodiments, the length L, width W, and/or thickness T of the glass or glass-ceramic articles may vary, such as for more complex geometries (see generally FIG. 4), where dimensions disclosed herein at least apply to aspects of the corresponding glass or glass-ceramic articles having the above-described definitions of length L, width W, and thickness T with respect to one another.

Accordingly, in some embodiments, such as depending upon particular applications or uses, at least one of the first or second surfaces 2112, 2114 has a relatively large surface area, that being at least 100 mm², such as at least 900 mm², at least 2500 mm², at least 5000 mm², at least 100 cm², at least 900 cm², at least 2500 cm², at least 5000 cm², and/or no more than 2500 m², such as no more than 100 m², no more than 5000 cm², no more than 2500 cm², no more than 1000 cm², no more than 500 cm², no more than 100 cm². As such, the glass or glass-ceramic article 2110 may have a relatively large surface area; which, except by methods disclosed herein, may be impossible to strengthen as disclosed herein with such thicknesses and/or surface quality, and/or strain homogeneity, without relying upon ion-exchange or a change in type of glass for the negative tensile stress portion of the stress profile (see generally FIG. 12).

According to contemplated embodiments, the strengthened glass or glass-ceramic article 2110 has a high-degree of dimensional consistency such that the thickness T thereof along a 1 cm lengthwise stretch of the body 2116 does not change by more than 50 μm, such as by not more than 10 μm, not more than 5 μm, not more than 2 μm. Such dimensional consistency may not be achievable for given thicknesses, areas, and/or magnitudes of negative tensile stress, as disclosed herein, by solid quenching due to practical considerations, such as cooling plate alignment and/or surface irregularities that may distort the dimensions.

According to contemplated embodiments, at least one of the first and second surfaces 2112, 2114 of the strengthened glass or glass-ceramic article 2110 is flat such that a 1 cm lengthwise profile therealong stays within 50 μm of a straight line, such as within 20 μm, 10 μm, 5 μm, 2 μm; and/or a 1 cm widthwise profile therealong stays within 50 μm of a straight line, such as within 20 μm, 10 μm, 5 μm, 2 μm. Such flatness may not be achievable for given thicknesses, areas, and/or magnitudes of negative tensile stress, as disclosed herein, by liquid quenching due to practical considerations, such as warping or bending of the strengthened glass or glass-ceramic article 2110 due to convective currents and associated forces of the liquid.

In another embodiment, the thermally strengthened glass sheets described herein have high flatness. The controlled gas bearing is preferably used in transporting and heating, and is used in cooling the sheet in various embodiments of processes and methods disclosed herein, resulting in higher degree of flatness than previously obtainable, particularly for thin and/or highly strengthened sheets. Sheets as thin as 0.55 mm were strengthened with a post-strengthening flatness of at least as good as 100 μm total indicator run-out (TIR), a measure of peak to valley distance measured along a length, within any 50 mm length, with 50 μm TIR within any 50 mm length routinely achievable. In contemplated embodiments, sheets with thickness disclosed herein the flatness 300 μm TIR or less within a 50 mm length on one of the first or second surfaces, such as flatness 200 μm TIR or less, flatness 100 μm TIR or less, flatness 70 μm TIR or less. In contemplated embodiments, sheets with thickness disclosed herein the flatness 200 μm TIR or less within a 20 mm length on one of the first or second surfaces, such as flatness 100 μm TIR or less, flatness 70 μm TIR or less, flatness 50 μm TIR or less.

Referring to FIG. 12, an conceptual stress profile 2210, at room temperature of 25° C. and standard atmospheric pressure, of the strengthened glass or glass-ceramic article 2110 of FIG. 7, shows an interior portion 2212 of the strengthened glass or glass-ceramic article 2110 under positive tensile stress and portions 2214 of the strengthened glass or glass-ceramic article 2110 exterior to and adjoining the interior portion 2212 under negative tensile stress. Applicants believe that the negative tensile stress at least in part fortifies the strengthened glass or glass-ceramic article 2110 by limiting initiation and/or propagation of cracks therethrough.

Believed unique to the present inventive technology given relatively large surface areas and/or thin thicknesses of the strengthened glass or glass-ceramic article 2110 as disclosed herein, tensile stress in the stress profile 2210 sharply transitions between the positive tensile stress of the interior portion 2212 and the negative tensile stress of the portions 2214 exterior to and adjoining the interior portion 2212 such that a rate of change (i.e., slope) of the tensile stress is at least a magnitude of stress (e.g., 100 MPa, 200 MPa, 250 MPa, 300 MPa, 400 MPa, a difference in peak values of the positive and negative tensile stresses +σ, −σ) divided by a distance, such as a distance of 1 mm, such as a distance of 500 μm, 250 μm, 100 μm (the is distance used to quantify a rate of change, not a dimension of the article geometry). In some such embodiments, the a rate of change of the tensile stress does not exceed 7000 MPa divided by 1 mm, such as no more than 5000 MPa divided by 1 mm. In contemplated embodiments, the difference in peak values of the positive and negative tensile stresses is at least 50 MPa, such as at least 100 MPa, at least 150 MPa, at least 200 MPa, at least 250 MPa, at least 300 MPa, at least 400 MPa, at least 500 MPa, and/or no more than 50 GPa. In contemplated embodiments, the glass or glass-ceramic article 2110 has a peak negative tensile stress of at least 50 MPa in magnitude, such as at least 100 MPa, at least 150 MPa, at least 200 MPa, at least 250 MPa, at least 300 MPa, at least 400 MPa, at least 500 MPa. Conventional thermal tempering approaches may be unable to achieve such steep tensile stress curves, indicative of ability to achieve higher magnitudes of negative tensile stress at a surface for a given thickness and/or to manufacture thinner articles to a higher degree of negative tensile stress, such as to achieve a fragmentation potential for dicing as disclosed herein.

According to an exemplary embodiment, the high rate of change of tensile stress is at least one of the above-described magnitudes or greater sustained over a thickness-wise stretch of the stress profile 2210 that is at least 2% of the thickness, such as at least 5% of the thickness, at least 10% of the thickness, at least 15% of the thickness, at least 25% of the thickness. In contemplated embodiments, the strengthening extends deep into the strengthened glass or glass-ceramic article 2110 such that the thickness-wise stretch with the high rate of change of tensile stress is centered at a depth of between 20% and 80% into the thickness from the first surface, which may further distinguish chemical tempering for example.

In at least some contemplated embodiments, the strengthened glass or glass-ceramic article includes a change in the composition thereof in terms of ion content, conceptually shown as dotted line 2216 in FIG. 12. More specifically, the composition of the strengthened glass or glass-ceramic article 2210 in such embodiments includes exchanged or implanted ions that influence the stress profile 2210. In some such embodiments, the exchanged or implanted ions do not extend fully through the portions 2214 of the strengthened glass or glass-ceramic article under the negative tensile stress because the negative tensile stress is also a result of the thermal tempering as disclosed herein.

Accordingly, the curve of the tensile stress profile 2210 with ion exchange strength augmentation includes a discontinuity or sudden change 2218 in direction where tangents of the curve differ from one another on either side of the discontinuity or sudden change 2218. The sudden change 2218 is located within the portions 2214 under negative tensile stress such that the tensile stress is negative on either side immediately adjacent to the discontinuity or sudden change 2218. The discontinuity or sudden change 2218 may correspond to the depth of the different ion content, however in some such embodiments other parts of the portions 2214 under negative tensile stress still have the same composition in terms of ion content as the portion 2212 under positive tensile stress.

Put another way, for at least some strengthened glass or glass ceramic articles 2110, with or without ion-exchange or implantation, the composition of the strengthened glass or glass-ceramic article 2110 at at least a part of the portions 2214 of the strengthened glass or glass-ceramic article 2110 exterior to and adjoining the interior portion 2212, under the negative tensile stress, is the same as the composition at at least a part of the interior portion 2212, under the positive tensile stress, such that at least some of the negative tensile stress of the stress profile is independent of a change in the composition of the strengthened glass or glass-ceramic article 2110. Such structure may simplify the composition of the strengthened glass or glass-ceramic article 2110 at least to a degree by providing sufficient strength without and/or with less chemical tempering. Further, such structure may reduce stress concentrations within the strengthened glass or glass-ceramic article 2110 due to discontinuity/changes in composition, possibly reducing chances of delamination and/or cracking at the composition discontinuity.

As discussed above, in some applications and embodiments, the strengthened glass or glass-ceramic article 2110 may have a composition configured for chemical durability. In some such embodiments, the composition comprises at least 70% silicon dioxide by weight, and/or at least 10% sodium oxide by weight, and/or at least 7% calcium oxide by weight. Conventional articles of such compositions may be difficult to chemically temper to a deep depth, and/or may be difficult if not impossible to thermally temper by conventional processes to a sufficient magnitude of negative tensile stress for thin thicknesses, such as due to fragility and forces of conventional processes. However, in contemplated embodiments, inventive processes disclosed herein allow a strengthened glass or glass-ceramic article 2110 with such a composition, where negative tensile stress extends into the respective strengthened glass or glass-ceramic article 2110 to a distance of at least 10% of the thickness of the strengthened glass or glass-ceramic article 2110 from at least one of the first and second surfaces 2112, 2114, such as at least 12% of the thickness, 15% of the thickness, 18% of the thickness, 20% of the thickness.

In some contemplated embodiments, the strengthened glass or glass-ceramic article 2110 may include an amorphous substrate, a crystalline substrate or a combination thereof, such as a glass-ceramic substrate. The strengthened glass or glass-ceramic article 2110 may include an alkali aluminosilicate glass, alkali containing borosilicate glass, alkali aluminophosphosilicate glass or alkali aluminoborosilicate glass. In one or more embodiments, the strengthened glass or glass-ceramic article 2110, in portions thereof not ion-exchanged, may include a glass having a composition, in mole percent (mol %), including: SiO₂ in the range from about 40 to about 80, Al₂O₃ in the range from about 10 to about 30, B₂O₃ in the range from about 0 to about 10, R₂O in the range from about 0 to about 20, and/or RO in the range from about 0 to about 15. In some contemplated embodiments, the composition may include either one or both of ZrO₂ in the range from about 0 mol % to about 5 mol % and P₂O₅ in the range from about 0 to about 15 mol %. In some contemplated embodiments, TiO₂ can be present from about 0 mol % to about 2 mol %.

In some contemplated embodiments, compositions used for the strengthened glass or glass-ceramic article 2110 may be batched with 0-2 mol % of at least one fining agent selected from a group that includes Na₂SO₄, NaCl, NaF, NaBr, K₂SO₄, KCl, KF, KBr, and SnO₂. The glass composition according to one or more embodiments may further include SnO₂ in the range from about 0 to about 2, from about 0 to about 1, from about 0.1 to about 2, from about 0.1 to about 1, or from about 1 to about 2. Glass compositions disclosed herein for the strengthened glass or glass-ceramic article 2110 may be substantially free of As₂O₃ and/or Sb₂O₃, in some embodiments.

In contemplated embodiments, example materials that may be used in strengthened glass or glass-ceramic article 2110 may include alkali aluminosilicate glass compositions or alkali aluminoborosilicate glass compositions, though other glass compositions are contemplated. Such glass compositions are capable of being chemically strengthened by an ion exchange process. One example glass composition comprises SiO₂, B₂O₃ and Na₂O, where (SiO₂+B₂O₃)≧66 mol. %, and/or Na₂O≧9 mol. %. In an embodiment, the glass composition includes at least 6 wt. % aluminum oxide. In a further embodiment, the strengthened glass or glass-ceramic article 2110 includes a glass composition with one or more alkaline earth oxides, such that a content of alkaline earth oxides is at least 5 wt. %. Suitable glass compositions, in some embodiments, further comprise at least one of K₂O, MgO, and CaO. In a particular embodiment, the glass compositions used in the strengthened glass or glass-ceramic article 2110 can comprise 61-75 mol.% SiO2; 7-15 mol.% Al₂O₃; 0-12 mol.% B₂O₃; 9-21 mol.% Na₂O; 0-4 mol.% K₂O; 0-7 mol.% MgO; and/or 0-3 mol.% CaO.

A further example glass composition suitable for the strengthened glass or glass-ceramic article 2110 comprises: 60-70 mol.% SiO₂; 6-14 mol.% Al₂O₃; 0-15 mol.% B₂O₃; 0-15 mol.% Li₂O; 0-20 mol.% Na₂O; 0-10 mol.% K₂O; 0-8 mol.% MgO; 0-10 mol.% CaO; 0-5 mol.% ZrO₂; 0-1 mol.% SnO₂; 0-1 mol.% CeO₂; less than 50 ppm As₂O₃; and less than 50 ppm Sb₂O₃; where 12 mol.%≦(Li₂O+Na₂O+K₂O)≦20 mol.% and/or 0 mol.%≦(MgO+CaO)≦10 mol.%. A still further example glass composition suitable for the strengthened glass or glass-ceramic article 2110 comprises: 63.5-66.5 mol.% SiO₂; 8-12 mol.% Al₂O₃; 0-3 mol.% B₂O₃; 0-5 mol.% Li₂O; 8-18 mol.% Na₂O; 0-5 mol.% K₂O; 1-7 mol.% MgO; 0-2.5 mol.% CaO; 0-3 mol.% ZrO₂; 0.05-0.25 mol.% Sn0 ₂; 0.05-0.5 mol.% CeO₂; less than 50 ppm As₂O₃; and less than 50 ppm Sb₂O₃; where 14 mol.%≦(Li₂O+Na₂O+K₂O)≦18 mol.% and/or 2 mol.%≦(MgO+CaO)≦7 mol.%.

In particular contemplated embodiments, an alkali aluminosilicate glass composition suitable for the strengthened glass or glass-ceramic article 2110 comprises alumina, at least one alkali metal and, in some embodiments, greater than 50 mol.% SiO₂, in other embodiments at least 58 mol.% SiO₂, and in still other embodiments at least 60 mol.% SiO₂, wherein the ratio (Al₂O₃+B₂O₃)/Σmodifiers (i.e., sum of modifiers) is greater than 1, where in the ratio the components are expressed in mol.% and the modifiers are alkali metal oxides. This glass composition, in particular embodiments, comprises: 58-72 mol.% SiO₂; 9-17 mol.% Al₂O₃; 2-12 mol.% B₂O₃; 8-16 mol.% Na₂O; and/or 0-4 mol.% K₂O, wherein the ratio (Al₂O₃+B₂O₃)/Σmodifiers (i.e., sum of modifiers) is greater than 1. In still another embodiment, the strengthened glass or glass-ceramic article 2110 may include an alkali aluminosilicate glass composition comprising: 64-68 mol.% SiO₂; 12-16 mol.% Na₂O; 8-12 mol.% Al₂O₃; 0-3 mol.% B₂O₃; 2-5 mol.% K₂O; 4-6 mol.% MgO; and 0-5 mol.% CaO, wherein: 66 mol.%≦SiO₂+B₂O₃+CaO≦69 mol.%; Na₂O+K₂O+B₂O₃+MgO+CaO+SrO>10 mol.%; 5 mol.%≦MgO+CaO+SrO≦8 mol.%; (Na₂O+B₂O₃)—Al₂O₃≦2 mol.%; 2 mol.%≦Na₂O—Al₂O₃≦6 mol.%; and 4 mol.%≦(Na₂O+K₂O)—Al₂O₃≦10 mol.%. In an alternative embodiment, the strengthened glass or glass-ceramic article 2110 may comprise an alkali aluminosilicate glass composition comprising: 2 mol % or more of Al₂O₃ and/or ZrO₂, or 4 mol % or more of Al₂O₃ and/or ZrO₂.

In contemplated embodiments, examples of suitable glass ceramics for the strengthened glass or glass-ceramic article 2110 may include Li₂O—Al₂O₃—SiO₂ system (i.e. LAS-System) glass ceramics, MgO—Al₂O₃—SiO₂ system (i.e. MAS-System) glass ceramics, and/or glass ceramics that include a predominant crystal phase including β-quartz solid solution, β-spodumene ss, cordierite, and lithium disilicate. The strengthened glass or glass-ceramic article 2110 may be characterized by the manner in which it is formed. For instance, where the strengthened glass or glass-ceramic article 2110 may be characterized as float-formable (i.e., formed by a float process), down-drawable and, in particular, fusion-formable or slot-drawable (i.e., formed by a down draw process such as a fusion draw process or a slot draw process).

A float-formable strengthened glass or glass-ceramic article 2110 may be characterized by smooth surfaces and consistent thickness is made by floating molten glass on a bed of molten metal, typically tin. In an example process, molten glass or glass-ceramic that is fed onto the surface of the molten tin bed forms a floating glass or glass-ceramic ribbon. As the glass ribbon flows along the tin bath, the temperature is gradually decreased until the glass or glass-ceramic ribbon solidifies into a solid glass or glass-ceramic article that can be lifted from the tin onto rollers. Once off the bath, the glass or glass-ceramic article can be cooled further and annealed to reduce internal stress. Where the glass or glass-ceramic article is a glass ceramic, the glass article formed from the float process may be subjected to a ceramming process by which one or more crystalline phases are generated.

Down-draw processes produce glass or glass-ceramic articles having a consistent thickness that possess relatively pristine surfaces. Because the average flexural strength of the glass or glass-ceramic article is controlled by the amount and size of surface flaws, a pristine surface that has had minimal contact has a higher initial strength. When this high strength glass or glass-ceramic article is then further strengthened (e.g., chemically), the resultant strength can be higher than that of a glass or glass-ceramic article with a surface that has been lapped and polished. Down-drawn glass or glass-ceramic articles may be drawn to a thickness of less than about 2 mm. In addition, down drawn glass or glass-ceramic articles have a very flat, smooth surface that can be used in its final application without costly grinding and polishing. Where the glass or glass-ceramic article is a glass ceramic, the glass or glass-ceramic article formed from the down draw process may be subjected to a ceramming process by which one or more crystalline phases are generated.

In some contemplated embodiments, thermally strengthened glass sheets disclosed herein have both high thermal stresses and low, as-formed surface roughness and/or coated surfaces. The processes and methods disclosed herein can thermally strengthen a sheet of glass without increasing the surface roughness of smooth as-formed or as-delivered surfaces of glass sheets, and likewise without damaging sensitive low-E or anti-reflective or other coatings. Incoming float glass air-side surfaces, and incoming fusion formed glass surfaces, were characterized by atomic force microscopy (AFM) before and after processing. Ra surface roughness was less than 1 nm (such as 0.6 to 0.7 nm) for incoming on the air side of 1.1 mm soda-lime float glass and was not increased by thermal strengthening according to the present disclosure. Ra surface roughness was less than 0.3 nm (such as 0.2 to 0.3 nm) incoming on 1.1 mm sheets of fusion formed glass and likewise was not increased by thermal strengthening according to this disclosure. Accordingly, in contemplated embodiments, thermally strengthened glass sheets according to this disclosure have surface roughness on a least a first surface in the range of at least 0.2 nm and/or no more than 1.5 nm Ra roughness, such as no more than 0.7 nm, such as no more than 0.4 nm or even such as no more than 0.3 nm, or thermally strengthened sheets having coatings thereon of the type that are preferably or necessarily applied before strengthening, or combinations of these low roughness values and coatings, are obtained from the present process used with corresponding glass sheets as starting material. It is Applicants' understanding that such preservation of surface quality and/or surface coating(s) previously required use of convective gas tempering or perhaps a low heat transfer liquid tempering process, which produces limited thermal strengthening effects relative to the total range available with the present processes and methods.

The fusion draw process, for example, uses a drawing tank that has a channel for accepting molten glass raw material. The channel has weirs that are open at the top along the length of the channel on both sides of the channel. When the channel fills with molten material, the molten glass overflows the weirs. Due to gravity, the molten glass flows down the outside surfaces of the drawing tank as two flowing glass films. These outside surfaces of the drawing tank extend down and inwardly so that they join at an edge below the drawing tank. The two flowing glass films join at this edge to fuse and form a single flowing glass article. The fusion draw method offers the advantage that, because the two glass films flowing over the channel fuse together, neither of the outside surfaces of the resulting glass article comes in contact with any part of the apparatus. Thus, the surface properties of the fusion drawn glass article are not affected by such contact. Where the glass or glass-ceramic article is a glass ceramic, the glass or glass-ceramic article formed from the fusion process may be subjected to a ceramming process by which one or more crystalline phases are generated.

The slot draw process is distinct from the fusion draw method. In slot draw processes, the molten raw material glass is provided to a drawing tank. The bottom of the drawing tank has an open slot with a nozzle that extends the length of the slot. The molten glass flows through the slot/nozzle and is drawn downward as a continuous glass article and into an annealing region. Where the glass or glass-ceramic article is a glass ceramic, the glass article formed from the slot draw process may be subjected to a ceramming process by which one or more crystalline phases are generated.

In some embodiments, the glass article may be formed using a thin rolling process, as described in U.S. Pat. No. 8,713,972, U.S. Pat. No. 9,003,835, U.S. Patent Publication No. 2015/0027169, and U.S. Patent Publication No. 20050099618, the contents of which are incorporated herein by reference in their entirety. More specifically the glass or glass-ceramic article may be formed by supplying a vertical stream of molten glass, forming the supplied stream of molten glass or glass-ceramic with a pair of forming rolls maintained at a surface temperature of about 500° C. or higher or about 600° C. or higher to form a formed glass ribbon having a formed thickness, sizing the formed ribbon of glass with a pair of sizing rolls maintained at a surface temperature of about 400° C. or lower to produce a sized glass ribbon having a desired thickness less than the formed thickness and a desired thickness consistency. The apparatus used to form the glass ribbon may include a glass feed device for supplying a supplied stream of molten glass; a pair of forming rolls maintained at a surface temperature of about 500° C. or higher, the forming rolls being spaced closely adjacent each other defining a glass forming gap between the forming rolls with the glass forming gap located vertically below the glass feed device for receiving the supplied stream of molten glass and thinning the supplied stream of molten glass between the forming rolls to form a formed glass ribbon having a formed thickness; and a pair of sizing rolls maintained at a surface temperature of about 400° C. or lower, the sizing rolls being spaced closely adjacent each other defining a glass sizing gap between the sizing rolls with the glass sizing gap located vertically below the forming rolls for receiving the formed glass ribbon and thinning the formed glass ribbon to produce a sized glass ribbon having a desired thickness and a desired thickness consistency.

In some instances, the thin rolling process may be utilized where the viscosity of the glass does not permit use of fusion or slot draw methods. For example, thin rolling can be utilized to form the glass or glass-ceramic articles when the glass exhibits a liquidus viscosity less than 100 kP. The glass or glass-ceramic article may be acid polished or otherwise treated to remove or reduce the effect of surface flaws.

In contemplated embodiments, the glass or glass-ceramic article 2110 has a composition that differs by side surface. On one side of the glass or glass-ceramic article 2110, an exemplary composition is: 69-75 wt % SiO₂, 0-1.5 wt % Al₂O₃, 8-12 wt % CaO, 0-0.1 wt % Cl, 0-500 ppm Fe, 0-500 ppm K, 0.0-4.5 wt % MgO, 12-15 wt % Na₂O, 0-0.5 wt % SO₃, 0-0.5 wt % SnO₂, 0-0.1 wt % SrO, 0-0.1 wt % TiO₂, 0-0.1 wt % ZnO, and/or 0-0.1 wt % ZrO₂. On the other side of the glass or glass-ceramic article 2110, an exemplary composition is: 73.16 wt % SiO₂, 0.076 wt % Al₂O₃, 9.91 wt % CaO, 0.014 wt % Cl, 0.1 wt % Fe₂O₃, 0.029 wt % K₂O, 2.792 wt % MgO, 13.054 wt % Na₂O, 0.174 wt % SO₃, 0.001 SnO₂, 0.01 wt % SrO, 0.01 wt % TiO₂, 0.002 wt % ZnO, and/or 0.005 wt % ZrO₂.

In other contemplated embodiments, composition of the glass or glass-ceramic article 2110 includes SiO₂ 55-85 wt %, Al₂O₃ 0-30 wt %, B₂O₃ 0-20 wt %, Na₂O 0-25 wt %, CaO 0-20 wt %, K₂O 0-20 wt %, MgO 0-15 wt %, BaO 5-20 wt %, Fe₂O₃ 0.002-0.06 wt %, and/or Cr₂O₃ 0.0001-0.06 wt %. In other contemplated embodiments, composition of the glass or glass-ceramic article 2110 includes SiO₂ 60-72 mol %, Al₂O₃ 3.4-8 mol %, Na₂O 13-16 mol %, K₂O 0-1 mol %, MgO 3.3-6 mol %, TiO₂ 0-0.2 mol %, Fe₂O₃ 0.01-0.15 mol %, CaO 6.5-9 mol %, and/or SO₃ 0.02-0.4 mol %.

Referring to FIG. 13, a glass or glass ceramic article 2310, having properties as disclosed herein with respect to the glass or glass ceramic article 2110, has been fractured, such as using a prick punch or other instrument and/or generally in accordance with American National Standards Institute (ANSI) Z97.1 (impact test) and the ASTM 1048 standard. According to an exemplary embodiment, the glass or glass ceramic article 2310 has been strengthened to a degree that dicing has occurred upon the fracture, forming a plurality of small granular chunks 2316 (e.g., fragments, pieces). In some embodiments, the glass or glass ceramic article 2310 has a thermally-induced stress sufficient to produce a number of granular chunks 2316 that is not less than 40 within an area of 50-by-50 mm of the glass or glass ceramic article 2310 in a fragmentation test in which an impact is applied with a hammer or a punch to initiate cracking of the glass into granular pieces. A standard office thumb tack 2312, with a metal pin length 2314 of about 1 cm is shown for reference.

According to various contemplated embodiments, despite the thin thickness of the strengthened glass or glass-ceramic article 2310, the stress profile (see generally FIG. 12) imparts a high fragmentation potential of the strengthened glass or glass-ceramic article 2310 such that when fractured the strengthened glass or glass-ceramic article 2310 shatters into particularly small granular chunks 2316, those having an area on either the first or second surface of less than 90 mm², such as less than 50 mm², such as less than 20 mm², such as less than 10 mm², such as less than 5 mm², and/or at least 10 μm². In some such embodiments, the fragmentation potential of the strengthened glass or glass-ceramic article 2310 is such that at least 20% (e.g., at least 50%, at least 70%, at least 95%) of the granular chunks 2316 have an area on at least one of the first or second surfaces of one of the above-described amounts when the strengthened glass or glass-ceramic article is fractured.

Due at least in part to the particularly thin geometry of the glass or glass-ceramic article 2310 that may be manufactured with the tensile stresses as disclosed herein using the inventive technology in some embodiments, the fragmentation potential of the strengthened glass or glass-ceramic article 2310 is such that, when fractured, the strengthened glass or glass-ceramic article 2310 shatters into particularly low-volume granular chunks, those having a volume of less than 50 mm³, such as less than 40 mm³, such as less than 30 mm³, such as less than 25 mm³, and/or at least a volume of 50 μm³.

Due at least in part to the particularly large area of the glass or glass-ceramic article 2310 that may be manufactured with the tensile stresses as disclosed herein using the inventive technology in some embodiments, the fragmentation potential of the strengthened glass or glass-ceramic article 2310 is such that, when fractured, the strengthened glass or glass-ceramic article 2310 shatters into at least 100 granular chunks 2316 of at least of 50 μm³ in volume, such as at least 200, at least 400, at least 1000, at least 4000 granular chunks 2316 of at least of 50 μm³ in volume.

According to an exemplary embodiment, the glass or glass-ceramic article 2110 has a portion thereof, such as at or near the first or second surface, that has a particularly high fictive temperature, such as at least 500° C., such as at least 600° C., or even at least 700° C. in some embodiments, such as for soda lime glass. According to an exemplary embodiment, the glass or glass-ceramic article 2110 has a portion thereof, such as at or near the first or second surface, that has a particularly high fictive temperature relative to annealed glass of the same chemical composition, such as at least 10° C. greater, at least 30° C. greater, at least 50° C. greater, at least 70° C. greater, or even at least 100° C. greater. High fictive temperature may be achieved by the presently disclosed inventive technology at least in part due to the rapid transition from the hot to the cooling zones. Applicants believe that high fictive temperature may corresponding or relate to increased damage resistance of glass. Surface fictive temperatures may be determined by any suitable method, including differential scanning calorimetry of pieces from the surface of the sheet and Brillouin and Raman spectroscopy. Stress may be relieved by breaking the sheet, otherwise stress effects will need to be deconvolved from the data if spectroscopic methods are used.

As may be seen in the table, Vickers crack initiation threshold is barely affected by conventional convective gas tempering (as reflected in the 6 mm sheet) rising from above zero but less than one Newton for annealed or as-delivered SLG sheets to above one but less than two Newtons for the thick sheets tempered at either level. This correlates with the relatively modest rise in surface fictive temperature (T_(fs)) of ˜25 to 35° C. relative to glass transition temperature (T_(g)) that was provided by conventional tempering. In contrast, by tempering using the present methods and apparatuses, T_(fs)-T_(g) was in the range of from approximately 75 to 90° C., at which levels the Vickers crack initial threshold improves to greater than 10 N, a 10-fold increase over the Vickers damage resistance imparted by conventional tempering. Lower levels of heat strengthening can still provide increased resistance, at levels such as 5 N, for instance. Non-destructive techniques for measuring surface or near-surface fictive temperature of thermally strengthened glass sheets are discussed in further detail below. In certain contemplated embodiments, Vickers crack initiation thresholds of greater than 5 N, 10N, 20N, and even 30N may be obtained.

Referring now to FIGS. 14-15, experiments were performed on 1.1 mm thick glass sheets of glass comprising at least 70% silicon dioxide by weight, and/or at least 10% sodium oxide by weight, and/or at least 7% calcium oxide by weight, strengthened using the equipment and processes disclosed herein. As shown in FIG. 14, the number of granular chunks 2316 per square centimeter of the glass has been found to be generally related to the magnitude of positive tensile stress at the center of the respective glass or glass-ceramic article 2310. Similarly, as shown in FIG. 15, the fragmentation potential of the respective glass or glass-ceramic article 2310 has also been found to be related to temperature of the glass in the hot zone (see FIGS. 9-10) and the calculated expected heat transfer coefficient (h) in units of cal/cm²·s·° C. (SI units watt/m²·° K) effectively applied to the glass surfaces during quenching, based on size of the gap between the glass sheet surfaces and the heat sink/gas bearing during quenching and on the thermal conductivity of the gas used in the gap.

In one experiment using inventive technology disclosed herein, a 5.7 mm thick sheet of glass comprising at least 70% silicon dioxide by weight, and/or at least 10% sodium oxide by weight, and/or at least 7% calcium oxide by weight was run with helium gas and gaps 204 a, 204 b (FIG. 8) of about 90 micrometers. The glass was heated to an initial temperature of about 690° C. and quickly cooled. The resulting strengthened article had a negative tensile stress of about 312 MPa on surfaces thereof and a positive tensile stress of about 127 MPa in the center. Also, the resulting strengthened article had a flatness of about 82.6 micrometers.

In another experiment using inventive technology disclosed herein, a 5.7 mm thick sheet of glass comprising at least 70% silicon dioxide by weight, and/or at least 10% sodium oxide by weight, and/or at least 7% calcium oxide by weight was run with helium gas and gaps 204 a, 204 b (FIG. 8) of about 90 micrometers. The glass was heated to an initial temperature of about 690° C. and quickly cooled. The resulting strengthened article had a negative tensile stress of about 317 MPa on surfaces thereof and a positive tensile stress of about 133 MPa in the center. Also, the resulting strengthened article had a flatness of about 89.7 micrometers.

In third experiment using inventive technology disclosed herein, a 5.7 mm thick sheet of glass comprising at least 70% silicon dioxide by weight, and/or at least 10% sodium oxide by weight, and/or at least 7% calcium oxide by weight was run with helium gas and gaps 204 a, 204 b (FIG. 8) of about 90 micrometers. The glass was heated to an initial temperature of about 690° C. and quickly cooled. The resulting strengthened article had a negative tensile stress of about 300 MPa on surfaces thereof and a positive tensile stress of about 121 MPa in the center. Also, the resulting strengthened article had a flatness of about 106.9 micrometers.

In another experiment using inventive technology disclosed herein, a 1.1 mm thick sheet of glass comprising at least 70% silicon dioxide by weight, and/or at least 10% sodium oxide by weight, and/or at least 7% calcium oxide by weight was run with helium gas and gaps 204 a, 204 b (FIG. 8) of about 56 micrometers. The glass was heated to an initial temperature of about 700° C. and quickly cooled. The resulting strengthened article had a negative tensile stress of about 176 MPa on surfaces thereof and a positive tensile stress of about 89.2 MPa in the center. Also, the resulting strengthened article had a flatness of about 190 micrometers.

In other experiments using inventive technology disclosed herein, 0.55 mm thick sheets comprising at least 70% silicon dioxide by weight, and/or at least 10% sodium oxide by weight, and/or at least 7% calcium oxide by weight was run with helium gas and gaps 204 a, 204 b (FIG. 8) of about 25 micrometers. The sheets were heated to an initial temperature of about 710° C. and 720° C. and quickly cooled. In both cases, the resulting strengthened article had a negative tensile stress of about 176 MPa on surfaces thereof and a positive tensile stress of about 63 MPa in the center. Also, the resulting strengthened articles had a flatness of about 168 (for the initial 710° C. temperature sample) and 125 micrometers (for the initial 720° C. temperature sample).

In one experiment using inventive technology disclosed herein, a 1.1 mm thick sheet of glass comprising at least 70% silicon dioxide by weight, and/or at least 10% sodium oxide by weight, and/or at least 7% calcium oxide by weight was run with helium gas and gaps 204 a, 204 b (FIG. 8) of about 160 micrometers. The glass was heated to an initial temperature of about 680° C. and quickly cooled. The resulting strengthened article had a negative tensile stress of about 112 MPa on surfaces thereof and a positive tensile stress of about 54 MPa in the center. Prior to strengthening, the sheet of glass had a flatness of about 96 micrometers, but the resulting strengthened article had a flatness of about 60 micrometers. Accordingly, the strengthening process also flattened the strengthened glass or glass ceramic article.

In another experiment using inventive technology disclosed herein, a 0.7 mm thick sheet of glass comprising at least 70% silicon dioxide by weight, and/or at least 10% sodium oxide by weight, and/or at least 7% calcium oxide by weight was run with helium gas and gaps 204 a, 204 b (FIG. 8) of about 31 micrometers. The glass was heated to an initial temperature of about 730° C. and quickly cooled. The resulting strengthened article had a negative tensile stress of about 206 MPa on surfaces thereof and a positive tensile stress of about 100 MPa in the center. Also, the resulting strengthened article had a flatness of about 82 micrometers.

In still another experiment using inventive technology disclosed herein, a 3.3 mm thick sheet of glass of borosilicate glass was run with helium gas and gaps 204 a, 204 b (FIG. 8) of about 120 micrometers. The glass was heated to an initial temperature of about 800° C. and quickly cooled. The resulting strengthened article had a flatness of about 120.5 micrometers.

The construction and arrangements of the glass and glass-ceramic, as shown in the various exemplary embodiments, are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes, and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations) without materially departing from the novel teachings and advantages of the subject matter described herein. Some elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process, logical algorithm, or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present inventive technology. 

What is claimed is:
 1. A strengthened glass or glass-ceramic article, comprising: a first surface, a second surface, and a body extending therebetween, wherein the second surface is on an opposite side of the body from the first surface such that a thickness of the strengthened glass or glass-ceramic article is defined as a distance between the first and second surfaces, a width of the strengthened glass or glass-ceramic article is defined as a first dimension of one of the first or second surfaces orthogonal to the thickness, and a length of the strengthened glass or glass-ceramic article is defined as a second dimension of one of the first or second surfaces orthogonal to both the thickness and the width; wherein the length of the strengthened glass or glass-ceramic article is greater than or equal to the width; wherein at least one of the first or second surfaces has a relatively large surface area, that being at least 2500 mm²; and wherein the strengthened glass or glass-ceramic article is thin such that the width is greater than five times the thickness; a stress profile of the strengthened glass or glass-ceramic article, wherein, at room temperature of 25° C. and standard atmospheric pressure, an interior portion of the strengthened glass or glass-ceramic article is under positive tensile stress and portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion are under negative tensile stress, whereby the negative tensile stress at least in part fortifies the strengthened glass or glass-ceramic article by limiting initiation and/or propagation of cracks therethrough; wherein a difference in peak values of the positive and negative tensile stresses is at least 200 MPa; and wherein, despite the relatively large surface area and thin thickness of the strengthened glass or glass-ceramic article, tensile stress in the stress profile sharply transitions between the positive tensile stress of the interior portion and the negative tensile stress of the portions exterior to and adjoining the interior portion such that a rate of change of the tensile stress is at least 200 MPa divided by a distance of 500 μm; and composition of the strengthened glass or glass-ceramic article, wherein the composition comprises (a) an amorphous, non-crystalline solid or (b) a polycrystalline solid comprising an amorphous phase and one or more crystalline phases; and wherein the composition comprises silicon dioxide; wherein the composition of the strengthened glass or glass-ceramic article located in at least a part of the portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion, under the negative tensile stress, is the same in terms of ion content and chemical constituency as the composition located in at least a part of the interior portion, under the positive tensile stress, such that at least some of the negative tensile stress of the stress profile is independent of a change in the composition of the strengthened glass or glass-ceramic article.
 2. The strengthened glass or glass-ceramic article of claim 1, wherein the rate of change of the tensile stress, that is at least 200 MPa divided by the distance of 500 μm, is at least maintained over a thickness-wise stretch of the stress profile that is at least 10% of the thickness.
 3. The strengthened glass or glass-ceramic article of claim 2, wherein strengthening extends deep into the strengthened glass or glass-ceramic article such that the thickness-wise stretch extends into a depth of between 20% and 80% into the thickness from the first surface.
 4. The strengthened glass or glass-ceramic article of claim 1, wherein the stress profile includes a rate of change of the tensile stress that is at least 200 MPa divided by a distance of 250 μm.
 5. The strengthened glass or glass-ceramic article of claim 4, wherein the difference in peak values of the positive and negative tensile stresses is at least 300 MPa, and wherein the stress profile includes a rate of change of the tensile stress that is at least 300 MPa divided by a distance of 250 μm.
 6. The strengthened glass or glass-ceramic article of claim 1, wherein the strengthened glass or glass-ceramic article has a value of the thickness that is no more than 1.7 mm.
 7. The strengthened glass or glass-ceramic article of claim 6, wherein the portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion have a peak value of the negative tensile stresses that is at least 200 MPa.
 8. The strengthened glass or glass-ceramic article of claim 6, wherein the strengthened glass or glass-ceramic article has a high-degree of dimensional consistency such that the thickness thereof along a 1 cm lengthwise stretch of the body does not change by more than 5 μm.
 9. The strengthened glass or glass-ceramic article of claim 6, wherein at least one of the first and second surfaces is flat such that a 1 cm lengthwise profile therealong stays within 2 μm of a straight line and a 1 cm widthwise profile therealong stays within 2 μm of a straight line.
 10. A strengthened glass or glass-ceramic article, comprising: a first surface, a second surface, and a body extending therebetween, wherein the second surface is on an opposite side of the body from the first surface such that a thickness of the strengthened glass or glass-ceramic article is defined as a distance between the first and second surfaces, a width of the strengthened glass or glass-ceramic article is defined as a first dimension of one of the first or second surfaces orthogonal to the thickness, and a length of the strengthened glass or glass-ceramic article is defined as a second dimension of one of the first or second surfaces orthogonal to both the thickness and the width; wherein the length of the strengthened glass or glass-ceramic article is greater than or equal to the width; wherein the width of the strengthened glass or glass-ceramic article is greater the thickness; and wherein the strengthened glass or glass-ceramic article is thin, having a value of thickness that is no more than 1 cm; a stress profile of the strengthened glass or glass-ceramic article, wherein, at room temperature of 25° C. and standard atmospheric pressure, an interior portion of the strengthened glass or glass-ceramic article is under positive tensile stress and portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion are under negative tensile stress, whereby the negative tensile stress at least in part fortifies the strengthened glass or glass-ceramic article by limiting initiation and/or propagation of cracks therethrough; wherein a difference in peak values of the positive and negative tensile stresses is at least 200 MPa; and wherein, despite the thin thickness of the strengthened glass or glass-ceramic article, the stress profile imparts a high fragmentation potential of the strengthened glass or glass-ceramic article such that when fractured the strengthened glass or glass-ceramic article dices into particularly small granular chunks, those having an area on either the first or second surface of less than 10 mm²; and composition of the strengthened glass or glass-ceramic article, wherein the composition comprises (a) an amorphous, non-crystalline solid or (b) a polycrystalline solid comprising an amorphous phase and one or more crystalline phases; and wherein the composition comprises silicon dioxide; wherein the composition of the strengthened glass or glass-ceramic article located in at least a part of the portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion, under the negative tensile stress, is the same in terms of ion content and chemical constituency as the composition located in at least a part of the interior portion, under the positive tensile stress, such that at least some of the negative tensile stress of the stress profile is independent of a change in the composition of the strengthened glass or glass-ceramic article.
 11. The strengthened glass or glass-ceramic article of claim 10, wherein the fragmentation potential of the strengthened glass or glass-ceramic article is such that at least 70% of the granular chunks have an area on at least one of the first or second surfaces that is less than 10 mm² when the strengthened glass or glass-ceramic article is fractured.
 12. The strengthened glass or glass-ceramic article of claim 10, wherein the fragmentation potential of the strengthened glass or glass-ceramic article is such that, when fractured, the strengthened glass or glass-ceramic article shatters into particularly small granular chunks, those having a volume of less than 30 mm³.
 13. The strengthened glass or glass-ceramic article of claim 12, wherein at least 70% of the granular chunks have a volume of less than 30 mm³ when the strengthened glass or glass-ceramic article is fractured.
 14. The strengthened glass or glass-ceramic article of claim 12, wherein the strengthened glass or glass-ceramic article fragments into at least 200 granular chunks of at least of 50 μm³ in volume when fractured.
 15. The strengthened glass or glass-ceramic article of claim 12, wherein the strengthened glass or glass-ceramic article has a value of thickness that is no more than 1.7 mm.
 16. The strengthened glass or glass-ceramic article of claim 15, wherein at least one of the first or second surfaces has a relatively large surface area, that being at least 2500 mm².
 17. The strengthened glass or glass-ceramic article of claim 16, wherein the portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion have a peak value of the negative tensile stresses that is at least 200 MPa.
 18. A strengthened glass or glass-ceramic article, comprising: a first surface, a second surface, and a body extending therebetween, wherein the second surface is on an opposite side of the body from the first surface such that a thickness of the strengthened glass or glass-ceramic article is defined as a distance between the first and second surfaces, a width of the strengthened glass or glass-ceramic article is defined as a first dimension of one of the first or second surfaces orthogonal to the thickness, and a length of the strengthened glass or glass-ceramic article is defined as a second dimension of one of the first or second surfaces orthogonal to both the thickness and the width; wherein the strengthened glass or glass-ceramic article has a value of length that is at least 3 cm; wherein the length of the strengthened glass or glass-ceramic article is greater than or equal to the width; wherein at least one of the first or second surfaces has a relatively large surface area, that being at least 2500 mm²; and wherein the strengthened glass or glass-ceramic article is thin such that the width is greater than five times the thickness; a stress profile of the strengthened glass or glass-ceramic article, wherein, at room temperature of 25° C. and standard atmospheric pressure, an interior portion of the strengthened glass or glass-ceramic article is under positive tensile stress and portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion are under negative tensile stress, whereby the negative tensile stress at least in part fortifies the strengthened glass or glass-ceramic article by limiting initiation and/or propagation of cracks therethrough; wherein a difference in peak values of the positive and negative tensile stresses is at least 200 MPa; and wherein, despite the relatively large surface area and thin thickness of the strengthened glass or glass-ceramic article, tensile stress in the stress profile sharply transitions between the positive tensile stress of the interior portion and the negative tensile stress of the portions exterior to and adjoining the interior portion such that a rate of change of the tensile stress is at least 200 MPa divided by a distance of 500 μm; and composition of the strengthened glass or glass-ceramic article, wherein the composition comprises (a) an amorphous, non-crystalline solid or (b) a polycrystalline solid comprising an amorphous phase and one or more crystalline phases; and wherein the composition comprises at least 70% silicon dioxide by weight; wherein the composition comprises at least 10% sodium oxide by weight; wherein the composition comprises at least 7% calcium oxide by weight; wherein, despite inclusion of sodium oxide and calcium oxide, the negative tensile stress extends into the strengthened glass or glass-ceramic article to a distance of at least 20% of the thickness of the strengthened glass or glass-ceramic article from a corresponding one of the of the first and second surfaces; and wherein the composition of the strengthened glass or glass-ceramic article located in at least a part of the portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion, under the negative tensile stress, is the same in terms of ion content and chemical constituency as the composition located in at least a part of the interior portion, under the positive tensile stress, such that at least some of the negative tensile stress of the stress profile is independent of a change in the composition of the strengthened glass or glass-ceramic article.
 19. The strengthened glass or glass-ceramic article of claim 18, wherein the strengthened glass or glass-ceramic article has a value of thickness that is no more than 1.7 mm.
 20. The strengthened glass or glass-ceramic article of claim 19, wherein the portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion have a peak value of the negative tensile stresses that is at least 200 MPa.
 21. The strengthened glass or glass-ceramic article of claim 18, wherein the strengthened glass or glass-ceramic article comprises a change in the composition thereof with respect to thickness such that the strengthened glass or glass-ceramic article comprises exchanged or implanted ions, at or near at least one of the first and second surfaces, that influence the stress profile but do not extend fully through the portions of the strengthened glass or glass-ceramic article under the negative tensile stress.
 22. A strengthened glass or glass-ceramic article, comprising: a first surface, a second surface, and a body extending therebetween, wherein the second surface is on an opposite side of the body from the first surface such that a thickness of the strengthened glass or glass-ceramic article is defined as a distance between the first and second surfaces, a width of the strengthened glass or glass-ceramic article is defined as a first dimension of one of the first or second surfaces orthogonal to the thickness, and a length of the strengthened glass or glass-ceramic article is defined as a second dimension of one of the first or second surfaces orthogonal to both the thickness and the width; wherein the length of the strengthened glass or glass-ceramic article is greater than or equal to the width; wherein the width of the strengthened glass or glass-ceramic article is greater the thickness; wherein the strengthened glass or glass-ceramic article is thin, having a value of thickness that is no more than 2 mm; wherein at least one of the first or second surfaces has a relatively large surface area, that being at least 5000 mm²; and wherein at least one of the first and second surfaces is flat such that a 1 cm lengthwise profile therealong stays within 2 μm of a straight line and a 1 cm widthwise profile therealong stays within 2 μm of a straight line; a stress profile of the strengthened glass or glass-ceramic article, wherein, at room temperature of 25° C. and standard atmospheric pressure, an interior portion of the strengthened glass or glass-ceramic article is under positive tensile stress and portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion are under negative tensile stress, whereby the negative tensile stress at least in part fortifies the strengthened glass or glass-ceramic article by limiting initiation and/or propagation of cracks therethrough; wherein a difference in peak values of the positive and negative tensile stresses is at least 250 MPa; and wherein, despite the thin thickness of the strengthened glass or glass-ceramic article, the stress profile imparts a high fragmentation potential of the strengthened glass or glass-ceramic article such that, when fractured, the strengthened glass or glass-ceramic article dices into particularly small granular chunks, those having a volume of less than 30 mm³; and wherein, despite the relatively large surface area and thin thickness of the strengthened glass or glass-ceramic article, tensile stress in the stress profile sharply transitions between the positive tensile stress of the interior portion and the negative tensile stress of the portions exterior to and adjoining the interior portion such that a rate of change of the tensile stress is at least 250 MPa divided by a distance of 500 μm; composition of the strengthened glass or glass-ceramic article, wherein the composition comprises (a) an amorphous, non-crystalline solid or (b) a polycrystalline solid comprising an amorphous phase and one or more crystalline phases; and wherein the composition comprises silicon dioxide; and wherein the composition of the strengthened glass or glass-ceramic article located in at least a part of the portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion, under the negative tensile stress, is the same in terms of ion content and chemical constituency as the composition located in at least a part of the interior portion, under the positive tensile stress, such that at least some of the negative tensile stress of the stress profile is independent of a change in the composition of the strengthened glass or glass-ceramic article.
 23. The strengthened glass or glass-ceramic article of claim 22, wherein at least 70% of the granular chunks have a volume of less than 30 mm³ when the strengthened glass or glass-ceramic article is fractured.
 24. The strengthened glass or glass-ceramic article of claim 22, wherein the strengthened glass or glass-ceramic article fragments into at least 200 granular chunks of at least of 50 μm³ in volume when fractured.
 25. The strengthened glass or glass-ceramic article of claim 22, wherein the stress profile includes a rate of change of the tensile stress that is at least 250 MPa divided by a distance of 250 μm, and wherein the rate of change of the tensile stress is at least maintained over a thickness-wise stretch of the stress profile that is at least 10% of the thickness.
 26. The strengthened glass or glass-ceramic article of claim 25, wherein strengthening extends deep into the strengthened glass or glass-ceramic article such that the thickness-wise stretch extends into a depth of between 20% and 80% into the thickness from the first surface.
 27. The strengthened glass or glass-ceramic article of claim 26, wherein the difference in peak values of the positive and negative tensile stresses is at least 400 MPa.
 28. The strengthened glass or glass-ceramic article of claim 26, wherein the portions of the strengthened glass or glass-ceramic article exterior to and adjoining the interior portion have a peak value of the negative tensile stresses that is at least 200 MPa.
 29. The strengthened glass or glass-ceramic article of claim 22, wherein at least one of the first and second surfaces has a flatness of less than 150 micrometers measured over a square centimeter.
 30. The strengthened glass or glass-ceramic article of claim 22, wherein the composition comprises at least 70% silicon dioxide by weight, at least 10% sodium oxide by weight, and at least 7% calcium oxide by weight; and wherein, despite inclusion of sodium oxide and calcium oxide, the negative tensile stress extends into the strengthened glass or glass-ceramic article to a distance of at least 20% of the thickness of the strengthened glass or glass-ceramic article from a corresponding one of the of the first and second surfaces. 